Validation of the diagnosis of mesothelioma and BAP1 protein expression in a cohort of asbestos textile workers from Northern Italy

Background: Diagnosis of mesothelioma based on death certificate is subject to misclassification, which may bias the results of epidemiology studies. A high proportion of mesothelioma harbor mutations in the BRCA1-associated protein 1 (BAP1) gene. Methods: We searched medical and pathology records and specimens for 127 workers from a textile-asbestos factory in Italy who died during 1963-2013 with a diagnosis of pleural or peritoneal neoplasm or mesothelioma on death certificate, to confirm the diagnosis with immunohistochemistry markers. We calculated the odds ratio of confirmation by selected characteristics and asbestos exposure variables. When sufficient pathology material was available, we analyzed BAP1 protein expression. Results: The diagnosis of mesothelioma was histologically confirmed for 35 cases (27.6%); 5 cases were classified as nonmesothelioma (3.9%), for 33 cases a mention of mesothelioma was found on record but no sufficient material was available for revision (26.0%); no records were available for 54 cases (death-certificate-only 42.5%). Diagnostic confirmation was not associated with sex, location of the neoplasm, age, or duration of employment; however, there was a significant association with time since first employment (P for linear trend 0.04). An association between duration of employment and time since first employment was observed for confirmed cases but not for death-certificate-only cases. BAP1 protein was lost in 18/35 cases (51.4%), without an association with sex, location, age, indices of asbestos exposure, or survival. Conclusions: We were able to confirm by immunohistochemistry a small proportion of mesothelioma diagnoses on certificates of deceased asbestos workers, and confirmation correlated with latency of asbestos exposure but not other characteristics. BAP1 protein loss is a frequent event in mesothelioma of asbestos-exposed workers, but does not correlate with exposure.